MYB Transcription Factors and a Putative Flavonoid Transporter ABCC-Like are Differentially Expressed in Radiata Pine Seedlings Exposed to Inclination

The response to inclination in plants is a well-studied biological process where hormones have been implicated in the modulation of vertical growth restoration. Studies on the involvement of auxins in differential growth of plant stems have resulted in the hypothesis that differential growth in stem tissue is due to unequal auxin re-distribution. It is known that flavonoids affect auxin distribution, but how the intracellular flavonoid concentration is controlled during the gravitropic response is unknown, especially in tree species. Due to the relationship between auxin, flavonoids, and transport during the response to inclination, genes coding for the control of flavonoid levels were identified and transcriptionally characterized in the transcriptome of pine seedlings exposed to inclination. Four MYB transcripts and one transcript encoding a transporter called PrMRP1 were identified and confirmed using qPCR. PrMRP1 has a high identity with specific transporters of flavonoids; its subcellular localization by fusion with green fluorescent protein and transient expression in tobacco was analyzed, confirming its location in the vacuolar membrane. These results suggest the involvement of MYBs and this transporter in regulating the distribution of flavonoids on the upper side of the stem at early stages of inclination.